Shoulder:Disorders of the Acromioclavicular Joint

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Bullet Points

  • Osteology: The acromioclavicular joint is a diarthrodial joint fibrocartilaginous. The intraarticular disc is located between the osseous segments.
  • Stability: The acromioclavicular ligament (superior, inferior, anterior, and posterior components) provides horizontal stability. The superior ligament is strongest, followed by posterior. The coracoclavicular ligaments (trapezoid and conoid) provides vertical stability. The trapezoid inserts 2.5 cm from end of clavicle. It is a stabilizer against horizontal and vertical loads. The conoid inserts 4.6 cm from end of clavicle in the posterior border more important ligament vertical stabilizer of acromioclavicular joint. The normal coracoclavicular distance (superior coracoid to inferior clavicle) is 11-13 mm. The deltotrapezial fascia, capsule, deltoid and trapezius act as additional stabilizers
  • Arthritis: The rate of asymptomatic acromioclavicular joint arthritis is high (65%) found the age of 40.
  • Distal clavicular osteolysis: this condition is classically seen in body builders.
  • Acromioclavicular joint dislocation: Surgery shoulder be considered only in high grade (4-5).

Key words

Acromioclavicular joint; Anatomy; Biomechanics; Arthritis; Distal clavicular osteolysis; Instability; Dislocation; Separation; Imaging; SAPHO syndrome; Distal clavicular osteolysis; Gorham-Stout disease; Conservative; Nonoperative Treatment; Stabilization; Reconstruction: Coracoclavicular cerclage; Mazzocca; Acute; Chronic; Complication.

Anatomical Considerations

The acromioclavicular joint that anchors the clavicle to the scapula. It is a diarthrodial joint that primarily rotates as well as translates in the anterior-posterior and the superior-inferior planes. The joint is surrounded by a capsule with synovium and an articular surface that is made up of hyaline cartilage containing an intra-articular meniscus-type structure. The mean width of the articular surface is 24.3+/-3 mm (range, 17-30 mm) for the acromial side and 24.6+/-3 mm (range, 17-30 mm) for the clavicular side.1 The mean anterior overhang of the acromion (anterior acromion-anterior joint distance) is 2.6+/-2.6 mm (range, 0-10 mm), whereas the mean anterior oversize of the clavicle (anterior clavicle-anterior joint distance) is 2.2+/-1.9 mm (range, 0-5 mm) (Figure). Only 60% of the acromioclavicular joints are aligned anteriorly, 3% have minor overhang of the acromion, 3% have minor overhang of the clavicle, 24% have major overhang of the acromion, and 10% have major overhang of the clavicle (Figure). Therefore, major misalignment anteriorly is found in 34% of the cases. The only reliable landmarks are the articular facets of both the acromion and the clavicle.

  1. Barth J, Boutsiadis A, Narbona P, et al. The anterior borders of the clavicle and the acromion are not always aligned in the intact acromioclavicular joint: a cadaveric study. J Shoulder Elbow Surg 2017;26:1121-7.
    Figure. 1 Photograph (a) and drawing (b) showing measurement methods. The anterior (A) and posterior (P) borders of the capsule are marked and connected with a straight line (AP line). Two parallel lines perpendicular to the AP line are created that passed through points A and P. Two anterior parallel lines perpendicular to the AP line are drawn: one passing at the most anterior edge of the acromion (acromion anteriorly [ACA]) and the other passing at the most anterior edge of the clavicle (clavicle anteriorly [CLA]). The same procedure is followed for the posterior part of the joint, and the lines passing from the acromion posteriorly (ACP) and clavicle posteriorly (CLP) were drawn. Reproduced with permission from Barth et al.
    The center of the conoid ligament inserts under the posterior part of the clavicle 46 mm medially to the acromioclavicular joint. The center of the trapezoid ligament has an anterior insertion under the clavicle, 25 mm medially to the acromioclavicular joint. The normal coracoclavicular distance (superior coracoid to inferior clavicle) is 11-13 mm.
  2. Renfree KJ, Wright TW. Anatomy and biomechanics of the acromioclavicular and sternoclavicular joints. Clinics in sports medicine 2003;22:219-37.
  3. Boehm TD, Kirschner S, Fischer A, Gohlke F. The relation of the coracoclavicular ligament insertion to the acromioclavicular joint: a cadaver study of relevance to lateral clavicle resection. Acta Orthop Scand 2003;74:718-21.
  4. Rios CG, Arciero RA, Mazzocca AD. Anatomy of the clavicle and coracoid process for reconstruction of the coracoclavicular ligaments. Am J Sports Med 2007;35:811-7.
    The acromioclavicular joint has dual innervation from both the suprascapular nerve and the lateral pectoral nerve.
  5. Miller M, Thompson S. Delee & Drez's Orthopaedic Sports Medicine: Principles and Practice: Elsevier; 2003.

Biomechanics of the Acromioclavicular Joint

The acromioclavicular joint is stabilized both by static and dynamic stabilizers. The static stabilizers include 1) the four acromioclavicular ligaments (superior, inferior, anterior, and posterior), 2) the lateral coracoclavicular ligaments (conoid and trapezoid), 3) the medial coracoclavicular ligaments (Figure and Video) and 4) the coracoacromial ligament.

  1. Stimec BV, Lädermann A, Wohlwend A, Fasel JH. Medial coracoclavicular ligament revisited: an anatomic study and review of the literature. Arch Orthop Trauma Surg 2012;132:1071-5.
  2. Moya D, Poitevin LA, Postan D, Azulay GA, Valente S, Giacomelli F, Mamone LA. The medial coracoclavicular ligament: anatomy, biomechanics,and clinical relevance-a research study. JSES Open Access. 2018 Sep 22;2(4):183-189.
    The latter, when transferred during standard Weaver-Dunn repair is only 1/4 as strong as the intact coracoclavicular ligaments; such technique of stabilization do not provide sufficient strength and is considered by many as obsolete.
  3. Weaver JK, Dunn HK. Treatment of acromioclavicular injuries, especially complete acromioclavicular separation. J Bone Joint Surg Am 1972;54:1187-94.
  4. Costic RS, Labriola JE, Rodosky MW, Debski RE. Biomechanical rationale for development of anatomical reconstructions of coracoclavicular ligaments after complete acromioclavicular joint dislocations. Am J Sports Med 2004;32:1929-36.
  5. Mazzocca AD, Santangelo SA, Johnson ST, Rios CG, Dumonski ML, Arciero RA. A biomechanical evaluation of an anatomical coracoclavicular ligament reconstruction. Am J Sports Med 2006;34:236-46.
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    The capsular ligaments acted as a primary restraint to posterior displacement of the clavicle. (Video)
  6. Fukuda K, Craig EV, An KN, Cofield RH, Chao EY. Biomechanical study of the ligamentous system of the acromioclavicular joint. J Bone Joint Surg Am 1986;68:434-40.[[File:Sensitive-content.png[500px]|frame|center|The superior ligament is strongest, followed by posterior. Both ligaments provide the most restraint to posterior translation of the acromioclavicular joint and must be preserved during a Mumford procedure. The coracoclavicular ligaments (trapezoid and conoid) provides vertical stability. The dynamic stabilizers include the deltoid and trapezius muscles.]]
  7. Abrassart S, Gagey O, Hoffmeyer P. La chape trapézo-deltoïdienne : réalité ou illusion d’optique. Revue de Chirurgie Orthopédique et Réparatrice de l'Appareil Moteur 2007;93:96-7.
    The coracoclavicular ligaments’ main contribution is to vertical stability. However, its double bundle configuration contributes also partially to horizontal stability due to their relative orientation.
  8. Lädermann A, Gueorguiev B, Stimec B, Fasel J, Rothstock S, Hoffmeyer P. Acromioclavicular joint reconstruction: a comparative biomechanical study of three techniques. J Shoulder Elbow Surg 2013;22:171-8.
  9. Yoo YS, Tsai AG, Ranawat AS, et al. A biomechanical analysis of the native coracoclavicular ligaments and their influence on a new reconstruction using a coracoid tunnel and free tendon graft. Arthroscopy 2010;26:1153-61.
    After lesion of the acromioclavicular ligaments, the conoid ligament acts as the primary restraint against anterior and superior loading, while the trapezoid functioned as the primary restraint against posterior loading.
  10. Debski RE, Parsons IMt, Woo SL, Fu FH. Effect of capsular injury on acromioclavicular joint mechanics. J Bone Joint Surg Am 2001;83-A:1344-51.
    When a load is applied in a superior direction, the conoid ligament fails first in its midsubstance region.
  11. Costic RS, Labriola JE, Rodosky MW, Debski RE. Biomechanical rationale for development of anatomical reconstructions of coracoclavicular ligaments after complete acromioclavicular joint dislocations. Am J Sports Med 2004;32:1929-36.
  12. Mazzocca AD, Spang JT, Rodriguez RR, et al. Biomechanical and radiographic analysis of partial coracoclavicular ligament injuries. Am J Sports Med 2008;36:1397-402.
    During elevation of the arm, the clavicle with respect to the thorax generally undergoes elevation (11-15 degrees), retraction (15 -29 degrees), and posterior long-axis rotation (15-31 degrees). Motion of the scapula (protraction-retraction) plays a major role in the motion at the acromioclavicular joint.
  13. Ludewig PM, Behrens SA, Meyer SM, Spoden SM, Wilson LA. Three-dimensional clavicular motion during arm elevation: reliability and descriptive data. The Journal of orthopaedic and sports physical therapy 2004;34:140-9.

Radiological or Radiographic Evaluation of the Acromioclavicular Joint

X-ray

Proper radiographic evaluation of the acromioclavicular joint requires multiple views. Zanca view is performed by tilting the x-ray beam 10° to 15° toward the cephalic direction. This view allows to analyze the acromioclavicular joint as well as the coracoclavicular interspace.

  1. Zanca P. Shoulder pain: involvement of the acromioclavicular joint. (Analysis of 1,000 cases). Am J Roentgenol Radium Ther Nucl Med 1971;112:493-506. The average distance between the clavicle and coracoid process is usually between 1.1 to 1.3 cm.
  2. Bosworth BM. Complete acromioclavicular dislocation. N Engl J Med 1949;241:221-5. An increase in the coracoclavicular distance of 25% to 50% over the normal side indicated complete coracoclavicular ligament disruption.
  3. Bearden JM, Hughston JC, Whatley GS. Acromioclavicular dislocation: method of treatment. J Sports Med 1973;1:5-17. The axial view of the shoulder was thought to be important in differentiating a type III from a type IV acromioclavicular joint injury. However, physiological misalignment between the anterior or posterior borders of the acromion and the clavicle exits.
  4. Barth J, Boutsiadis A, Narbona P, et al. The anterior borders of the clavicle and the acromion are not always aligned in the intact acromioclavicular joint: a cadaveric study. J Shoulder Elbow Surg 2017;26:1121-7. This finding explains probably why the axial view is not reliable and should not isolated be taken into account when planning a surgery.
  5. Gastaud O, Raynier JL, Duparc F, Baverel L, Andrieu K, Tarissi N, Barth J. Reliability of radiographic measurements for acromioclavicular joint separations. Orthop Traumatol Surg Res. 2015 Dec;101(8 Suppl):S291-5.
  6. Rahm S, Wieser K, Spross C, Vich M, Gerber C, Meyer DC. Standard axillary radiographs of the shoulder may mimic posterior subluxation of the lateral end of the clavicle. J Orthop Trauma. 2013 Nov;27(11):622-6.

Alexander view demonstrate acromioclavicular instability (Figures).

Left pathologic Alexander views
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